Method of making milling-cutters



F. MULLER.

METHOD OF MAKING MILLING CUTTERS. I APPLICATION FILED MAR. 31, 1919. 1,348,309. PatentedAug. 3,1920.

' 4 SHEETS-SHEET l.

F. MULLER.

I METHOD OF MAKING MILLING CUTTERS.

APPLICATION TILED MAR. 31, 1919.

1,348,309. Patented Aug. 3,1920.

4 SHEETS-SHEET 2.

INVENTOR v a AT 0 NEY F. MULLER.

METHOD OF MAKING MILLING CUTTERS.

APPLICATION FILED MAR. 31. I9I9.

'1 348 309 Patented Aug. 3, 1920.

4 SHEETSSHEET 3.

ayaa- INVENTOR adamamum'- w T RNEY F. MULLER.

METHOD OF MAKING MILLING CUTTERS. APPLICATION FILED MAR. 31, 1919.

'1 ,348,309 Patented Aug. 3, 1920.

4 SHEETS-SHEET 4.

FAA-M Aw BY O RNEY UNITED STATES PATENT caries.

FRIEDERICH MIILLER, OF HARTFORD, CONNECTICUT, ASSIGNOR T0 PRATT & WHITNEY COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

METHOD OF MAKING MILLING-CUTTERS.

Specification of Letters Patent.

Patented Aug. 3, 1920.

Application filed March 31, 1919. Serial No. 286,523,

a citizen of the United States, residing at Hartford, in the county of Hartford and State of Connecticut, have invented certain new and useful Improvements in Methods of Making Milling-Cutters, of which the following is a specification.

It is a well known principle in the art of cutting metals that the cutting edge of the tool should preferably be inclined with respect to the direction of relative movement so as to effect a shearing cut. This inclination is of advantage in that it improves the cutting action and it is also of advantage 1n that it permits the tool to engage the work gradually and with relatively little shock instead of engaging it suddenly with greater shock. This principle has been applied to relieved milling cutters which are of uniform diameter throughout and has also been applied to milling cutters having a uniform taper from one end to the other. These milling cutters have their cutting edges longitudinally inclined with respect to the axis,

the cutting edge usually approximately-conforming to a helix. Thus each tooth is enabled to engage the work gradually and to effect a shearing cut.

I have applied this principle to accurately made and properly relieved formed or contour cutters. By a formed or contour cutter I mean one in which the diameter varies from end to end inways differing from a uniform taper, the cutter being thus adapted to cut a predetermined contour other than a straight line. Prior to my invention it had not been deemed practical or possible to make.such cutters with inclined cutting faces. The said invention is presented and claimed in my copending application for milling cutters, Serial No. 268,349, filed Decem'ber 26th, 1918.

In my copending application for milling "cuttersQSerial No. 286,521, filed on even date herewith, I have presented a milling cutter embodying the invention set forth in my said application, Serial No. 268,319, but having certain additional features of improvement adapting it for special kinds'of work. WVith a cutter such as a gear cutter having a very deep contour, the advantages arising from the inclination of the cutting faces in accordance with my invention set forth in application, Serial 'No. 268,3 t9, may be partly offset by the fact that, while the cutting edges at one side are, formed at acute angles, those at the other side are formed at obtuse. angles. These latter cutting edges not only fail to out easily but tend to crowd the cutter bodily toward the other side. In accordance with the invention set forth in application Serial No. 286,521, I provide the cutter with cutting faces which are inclined oppositely, the cutting faces inclined in one direction preferably being arranged alternately with respect to those in- .clined in the opposite direction. Also in accordance with the said invention the cutter is so formed that each tooth is effective for cutting only at the acute-angled side thereof and is ineffective for cutting at the obtuseangled side thereof.

The object of the present invention is to provide a method of making milling cutters embodying the invention set forth in my said application Serial No. 286,521.

As to a part of its subject matter the present application constitutes a continuation of my abandoned application for milling cutters and methods of making, Serial No. 237,705, filed June 1st, 1918.

In the accompanying drawings I have shown two different cutters, and I have illustrated two forms of method which may be used for making the cutters. It will be understood, however, that the drawings are intended to be merely illustrative and are not to be construed as defining or limiting the scope. of the invention, the-accompanying claims being relied upon for that purpose. Particularly it will be understood that there can be wide variation in the contours of the cutters, the contours shown being merely selected as typical.

Of the drawings:

Figures 1 and 2 are plan and side views respectively of a milling cutter embodying the invention. A gear cutter has been selected for purposes of illustration.

Fig. 3 is"a fragmentary developed sectional view taken along the arcuate line principles of the invention Figs. 8 and 9 are fragmentary dia ram 4 matic views, similar respectively to and 5, illustrating a cutter similar to that shown in the said figures but differing therefrom in certain respects.

Figs. 10 and 11 are diagrammatic views illustratin certain features of the cutter shown in Figs. 8 and 9.

Figs. 12 and 13 are fragmentary side and bottom views respectively of a preliminary milling cutter adapted to be used in makin the final cuttershown in Figs. 4 and 5.

Fig. 14 is a diagrammatic view illustrat' ing certain features of the preliminary cutter shown in Figs. 12 and 13.

Figs. 15 and 16 are fragmentary side and bottom views respectively of another preliminary milling cutter adapted to be used in making the final cutter shown in Figs. 4 and- 5.

Fig. .17 is a diagrammatic view illustrating certain features of the preliminaryv cutter shown in Figs. 15 and 16.

Figs. 18 and 19 are fragmentary side and bottom views respectively of a preliminary milling cutter adapted to be used inv making the final cutter shown in Figs. 8 and 9.

Fig. 20 is a plan view of a lathe.tool adapted to be used for shaping the preliminary milling cutters.

ig. 21 is a diagrammatic view illustrating a. method of shaping a preliminary milling cutter, use being made ofthe lathe tool [shown in Fig. 20.

Fig. 22 is a diagrammatic view illustrating the preliminar cutter shown in F igs. 12 and 13 in use or milling a tooth of a blank for the final cutter shown in Figs. 4 and 5, the milling operation having been started but not finished.

Fig. 23 is a view similar to Fig. 22 but illustrating the tooth completelv milled.

F ig. 24 is a view similar to Fig. 22 illustrating the preliminary cutter shown in Figs. 15 and 16 in use for milling another tooth of the blank for the final cutter shown in Figs. 4 and 5, the milling operation having been started but not finished.

Fig. 25 is a view similar to Fig. 24 but illustrating the tooth completely milled.

Figs. 26 and 27 are diagrammatic views illustrating the' preliminary cutter shown in Figs. 18 and 19 in use for milling a tooth of the blank for the final cutter shown in Figs. 8 and 9.

Figs. 28and 29 are plan and side views respectively of a single tooth formed by the method step illustrated in Figs. 26 and 27.

Figs. 30 and 31. are views similar respec tively to Figs. 26 and 27 illustrating the preliminary cutter shown in Figs. 18 and 19 in use for milling another tooth of the blank for'the final cutter shown in Figs. 8 and 9.

Figs. 32 and 33 are plan and'side views respectively of a single tooth made by the method step illustrated in Figs. 30 and 31.

In order that the methods may be clearly understood I have shown in the accompanying drawings two different cutters embodying the invention set forth in the aforesaid application Serial No. 286,521. Referring to the'drawings, particularly to Figs. 1 to 5 thereof it will be seen that I have shown a cutter A embodying the invention, a gear cutter having been selected by way of example. The cutter A is provided with two sets of generally lon itudinal teeth 1 and 2 with. grooves 3 an 4 between them. The teeth and grooves are preferably spaced uniformly, or approximately so. The grooves can be of any usual or preferred depth and shape, as required by the slpacing and by the depth of the contour. he front walls 5 and 6 of the teeth 1 and 2 respectively constitute cutting faces and these. cutting faces are radial or approximately so in order to provide a satisfactory cutting angle. In accordance with the invention, the cutting faces 5 and 6 are inclined or positioned obliquely so that the longitudinal lines of each of them lie at an les to the axis of the cutter. The cutting faces 5 of the teeth 1 are inclined in one direction and the cutting faces 6 of the teeth 2 are inclined in the other direction. By preference the teeth 1' and 2 with the respective cutting faces 5 and 6 oppositely inclined are alternated with each other, as clearly shown in the drawings. Preferably the entire grooves 3 and 4 are oblique or inclined the rear wall of each tooth being inclined in the same direction as the front wall of the next following tooth and in the opposite direction from its own front wall. Each cutting face preferably conforms to a helicoid, and as illustrated each helicoid is one formed by a generatrix following the axis of the cutter and also following a helix on a cylinder concentric with the axis thereof, the helicoid in this case being radial. The helicoids for the different cutting faces 5 and 6 are oppositely inclined but preferably the de r'ees of inclination and the longitudinal pltches are the same.

The cutter may be made for cutting any desired practical contour. The contour illustrated is that of the space between two teeth of a spur gear, and the invention is particularly applicable to a cutter, such as a gear cutter, having a contour which is symmetrical or approximately so. 1

,With a cutter such as shown having a deep convex contour, it is obvious that a large part of the cutting will be effected at the sides of the teeth. The cutting angles at the sides of the teeth are therefore important. Fig. 3 is a developed fragmentary sectional view of the cutter A, the direction of movement during operation being indicated by the arrow. This View shows more clearly the inclination of the grooves 3 and 4, and of, the cutting faces 5 and 6. It will be seen that a tooth 1 behind one of the grooves '3 has at one side,

i in this case the foremost side, an angle 6 which is acute and well adapted for cutting. The same tooth 1 has at the other side, in this case the rearmost side, an angle 7 which is obtuse and not well adapted for cutting. It will therefore be seen that, if all the teeth were the same, one side of the cutter, that is the side having the angles 0, would be much better for cuttin than the other side having the angles f. he f side would not only cut poorly but would tend to force the cutter endwise toward the 6 side. These disadvantages are overcome by the oppositely formed teeth 2 each of which has an angle e and an angle f on the sides opposite respectively to the angles e and the angles 7' of the teeth 1. As before stated, the respective teeth 1 and 2 are preferably alternately arranged.

It will be noted that the foregoing discussion as to the anglese and f is wholly applicable only to a cutter having a convex contour. For a cutter having a concave contour the acute-angled side of each tooth is to the rear of the obtuse-angled side instead of in advance thereof, and the invention is therefore less advantageous as applied to such a cutter.

The outer edge of each cutting face has an outline which is shaped to out either all or at least a part of the predetermined contour when the cutter is rotated, this outline of the cutting face following the helicoidal surface thereof. ,Each cutting face 5 or 6 of the cutter A has an outline such that each tooth will cut the entire predetermined contour, as shown by full lines in Figs. 6 and 7. This outline includes the points 21, 22, 23, 24 and 25. All points along the outline are at their respective correct distances from the center so that when the cutter is rotated they will define the correct predetermined contour. This relationship of the several points along the cutting face.

standing the variations in radius at different points along the said outline and notwithstanding the variations in angular position resulting from the warped or helicoidal cutting face. Preferably the relief lines 7 or '8 of each tooth are maintained in similar relationship to each other as they extend backward and inward, the lines preferably conforming to spirals of Archimedes.

As the result of the spiral relief each tooth 1,'at any axial plane of intersection, such as 6-6, has a distorted shape, as shown by dotted lines in Fig. 6. This distorted shape includes points 31, 32, 33, 34 and 35 corre-' sponding respectively to the points 21, 22, 23, 24 and 25 onthe outline of the cutting face 5. The distortion of shape results from the fact that the successive inward inclined relief lines 7 start at different angular positions because of the inclined or helicoidal Therefore with the cutting face 5 inclined in the direction shown the several points 34, 33, 32 and 31 to the left of the point 25 or 35 are spaced inward from the respective points 24, 23, 22 and'21 by progressively increasing distances. Notwithstanding this distortion in shape at an axial plane of intersection, the outline or effective contour at the cutting face 5 is correct, as before stated. Similarly each tooth 2, at any axial plane of intersection, such as 7-7, has a distorted shape as shown by dotted lines in Fig. 7 This distorted shape includes points 41, 42, 43, 44 and 45 corresponding respectively to the points 21, 22, 23, 24 and 25 on the outline of the cutting face 6. With the cutting face 6 inclined in the direction shown the several points 42,- 43, 44 and 45 to the right of the point 21 or 41 are spaced inward from the respective points 22, 23, 24 and 25 by progressively increasing distances. Notwithstanding this distortion in shape at an axial plane of intersection, the outline or effective contour at the cutting face 6 is correct, as before stated. Inasmuch as all of the teeth have an effective contour, which is the same as the predetermined contour, the cutter will cut the said predetermined contour when used.

When the relief lines 7 and 8 conform to spirals and are maintained in similar relationship as they extend backward and inward, as is preferred, it is possible to sharpen or grind the teeth of the cutter on the front cutting faces 5 and 6 without changing the effective contour. The teeth present the same effective contour at successive inclined surfaces of intersection similar in form and position to the initial cutting faces. At any surface, such as gg, back of the initial cutting face 5 of a tooth 1 and similar to the said face, the same effective contour will be found. Similarly at anysurface, such as h-h back of the initial cutting face 6 of a tooth and similar to I the said face, the same effective contour will be found. Therefore if the cutter is ground on the front faces to helicoids which are the same as the helicoids of the initial cutting faces the effective contour will remain the same.

.of cutting only at the acute-angled side,

the obtuse-angled side being reduced so as to rovide a clearance.

he teeth 9 and 10 of the cutter B are separated by grooves 11 and 12 and the teeth are provided respectively with cutting faces 13 and 14 similar respectively to the' faces the left.

5 and 6 of the cutter A. The teeth are relieved respectively along spiral lines 15 and 16. The cutter B is or ma be similar to the cutter A exce t as hereinafter described. As shown by ull lines in Fig. 10, the cutting face 13 of each tooth 9 has at its left acute-angled or foremost side an outline 21, 22, 23 such that the tooth will cut at least the left half of the predetermined contour 21, 22, 23, 24, 25. The right obtuse-angled or rearmost side has an outline which is slightly reduced below the desired contour, the amount of reduction gradually increasincg1 from the center toward the right. The

iced outline at the right is indicated by '23, 24", 25". As shown by full lines in Fig.

11 the cutting face 14 of each tooth 10 has at its right acute-angled or foremost side an outline 23, 24, 25 such that the tooth will out at least the right half of the predetermined contour 21, 22, 23, 24, 25. The left obtuse-angled or rearmost side has an outline which is slightly reduced below the desired contour, the amount of reduction gradually increasing from the center toward The reduced outlineat the left is indicated by 23, 22 21.

Each tooth 9 at any axial plane of intersection, such as 10-l0, has a distorted shape 31, 32, 33, 34 and 35", as shown by dotted lines in Big. 10. The shape 31, 32, 33 at the left is the same as the left half of the shape 31, 32,33, 34, 35 of a tooth 1 of the cutter A as shown in Fig. 6, but the shape 33, 34, 35 at the right is reduced below the said shape 31, 32, 33,-34, 35, the amount of reduction gradually increasing from the center toward the right. Each tooth 10 at any axial plane of intersection, such as 11-11,

has a distorted shape 41", 42", 43, 44 and 45, as shown by dotted lines in Fig. 11. The shape 43, 44, 45 at the right is the same as the right half of the shape 21, 22, 23, 24, 25 of a tooth 2 of the cutter A as shown in -Fig. 7, but the shape 43, 42 and 41 at the left is reduced below the said shape 41, 42, 43, 44, 45, the amount of reduction gradually increasing from the center toward the left. Inasmuch as each alternate tooth has an effective contour which is the same as oneing the effective contour.

Taking up now the method of making the improved milling cutter, it will be understood that the preliminary steps of turning the blank, cutting the grooves therein, etc,, can be carried on in any usual or preferred way, these not of themselves constituting any part of the present invention. tion relates particularly to the method of shaping the blank to provide the right-hand and left-hand teeth with distorted contours which will cut a correct contour.

The method is in many respects similar to that set forth in my copending application for methods of making milling cutters, Serial No. 268,350, filed December 26th, 1918.

The inven- Reference may be had to the said application for detailed description of certain phases of the method and of certain possible variations thereof.

In practising the method there is provided a preliminary cutting means which may be either one or two preliminary cutters adapted to be used to form the shape of the final milling cutter. Preferably the preliminary cutters are milling cutters and they will be so described. For making the cutter A use is made of two milling cutters R and S, shown respectively in Figs. 12 to 14 and 15 -to 17. For making the cutter B use is preferably made of a single milling cutter T shown in Figs. 18 and 19.

The cutter R is provided with generally longitudinal teeth 46 which are separated by grooves 47 and which have front cutting faces 48. Each tooth of the preliminary cutter R has at any axial plane of-intersection such as 14,14 a shape which is the same or approximately the same as the predetermined contour, as shown by dotted lines in Fig. 14. While the contour is the same, it is reversely positioned with respect to the axis, the points which are outermost on the final cutter being innermost on the preliminary cutter and vice versa. The points along this plane of intersection are indicated by 21, 22 23, 24 and 25 these corresponding respectively to the points '21, 22, 23, 24 and 25 on the effective contour of the final cutter A.

The front cutting faces 48 of the teeth 46 of the cutter R are helicoidal in form and have the same longitudinal pitch or lead as the helicoidal faces 5 of the teeth 1 of the cutter A. The cutting faces 48 and the cutting faces 5 are inclined in the same direction. The preliminary cutter R is preferably much smaller in diameter than the final cutter, and therefore there is an apparent difference in the helicoidal surfaces ofthe two cutters. lNhile the helicoids are in realitv the same, being determined by the same or similar directrices, the actual angle of inclination is less for the preliminary cutter l than for the final cutter A because of the smaller diameter. The actual angle of inclination of the cutting faces of the preliminary cutter is immaterial, and therefore the diameter of the preliminary cutter R can be varied as desired without interfering with the practice of the method. For the cutter A as illustrated in Figs. 6 and 7 the length i of the cutter may be taken as the unit of length, and it will be seen that the corresponding angular advance is represented by i. F or the cutter R as illustrated in Figs. 12 and 13 the same unit of length 2' is taken, and the angular advance j is kept thesame.

Each tooth 46 of the preliminary cutter L has a degree of relief which is the same as the degree of relief of the teeth of the final cutter. The degree of relief in each case is represented by the ratio between the angular advance of the cutter and the decrease in diameter. The decrease in diameter for each angular increment of advance of the cutter R is the same as the decrease in diameter for each angular increment of advance of the cutter A. While the degrees of relief are the same for both cutters, there is an apparent difference because of the smaller diameter of the cutter R. This causes the relief lines to meet the circumferential lines at a relatively small angle such as Z: for the (utter A and at a relatively large angle such as 7r for the cutter R, but it will be remembered that the degrees of relief are the same,

as before explained.

As the result of providing the teeth of the preliminary cutter R with the same helicoidal cutting faces and with the same degree of relief as the teeth 1 of the final cutter A, the front outline or effective contour of each tooth is distorted, as shown by full lines in Fig. 14. The points 313' 32?, 33 34 and 35' along the distorted outline correspond respectively to the points 21', 22, 23 24 and 25 along the shape at an axial plane of intersection. The several points 34, 33', 32 and 31 to the right of the point 25" or 35 are spaced outward from the respective points 34, 33, 32 and 31by progressively increasing distances. The actual inclination of each cutting face is less by reason of the smaller diameter but the amount of relief is more for the same reason, and these differences exactly compensate for each other. The result is that the distortion of the outlines 31 32, 33 34 35 of the teeth of the cutter R is exactly the reverse of the desired distortion 31, 32, 33, 34, 35 of the teeth 1 of the final cutter A along axial planes of intersection, the two distortions being'exactly the same in extent.

The cutter S has teeth 49 with grooves 50 between them, the teeth being provided with helicoidal cutting faces 51. The cutter S is exactly like the cutter R except that the cutting faces 51 are inclined in the direction opposite to that of the cutting faces 48. Each tooth of the preliminary cutter S has at any axial plane of intersection such as 17-17 a shape which is the same or approximately the' same as the predetermined contour, as shown by dotted lines in Fig.

17, and also the same as the shape 21", 22%.

23", 24, 25 of the tooth of the cutterR.

The points along this plane are indicated by 21 22 23 24 and 25. The distorted front outline or effective contour of each tooth is 41 42 43 44 and 45 the several points the two distortions being exactly the same in extent. a

The cutter T has differing teeth 46 and 49 with grooves 52 and 53 between them,

the teeth being providedrespectively with helicoidal cutting faces 48 and 512 Each tooth 46 is similar to .a tooth 46 of the cutter R, and each tooth 49 is similar to a tooth 49 of the cutter S. Each tooth 46 has a distorted front outline or effective contour 31*, 32, 33, 34, and-35 which is the same as the contour 31, 323.33, 34, 35 of the cutter R. Each tooth 49 has a distorted front outline or effective contour 41', 42,

43, 44v and 45 which is the same as the contour 41, 42", 43, 44', 45 of the cutter S. Any of the preliminary cutters R, or T can most conveniently be made by means of a lathe tool such as V, shown 1n Figs.

20 and 21, this tool bein used in a relieving lathe. The lathe tool is formed with a contour 21", 22", 23 24" and 25 on its top cutting face which is the same as the effective contour of the teeth of the final cutter A. Fig. 21 shows the cutter B being v50 46, of the rotatin formed, it being understood that it is ro tated in the direction of the arrow and that the tool V is moved in and out, as indicated by the horizontal arrow, so as to follow the proper relief. The operation is exactly the in Fig. 21.

In makin the cutter A both of the cutters R and are'used, as shown in Figs. 22

to 25. Either cutter may be used first and 20 I will first describe the use of the cutter R.

Figs. 22and 23 show the preliminary cutter R in use for milling the teeth 1 of the final cutter A. It will be understood that the cutter R is rapidly rotating in the direction indicated by the arrow thereon; that the blank A is slowly rotating in the direction indicated by the arrow thereon; and that relative approaching and receding. movements are effected between the cutter and the blank in timed relation to the blank rotation to provide the required relief on the final cutter. These relieving movements are preferably effected by moving the axis of the cutter bodily toward the axis of the blank, as indicated by the vertical arrow, and then bodily away from the axis of the blank in the opposite direction. Preferably the downward or inward relieving movement is so timed that the resultin re- 40 lief on the blank will conform to spiras of Archimedes. The cutter R is moved slowl downward during the cutting of each toot 1 and then is rapidly moved upward between the teeth to position it for the cutting of the next-tooth 1. The timing of f the relieving movements is such that the teeth 2 are not engaged.

As shown in Fig. 22, the cutter R and the blank A have been '50 adjusted that the teeth cutter D will mill the initial point 21 o the tooth 1 of the blank A to the required distance from the axis. The downward movement of the cutter R in timed relation to the slow rotation of the blank A causes it to take a cut which gradu- 66 distances from the axis so that these teeth teeth 9", the teeth 9 when used will cut the true predetermined contour, as shown by full lines in Fig. 6.

The action of the cutter S as shown in Figs. 24 and 25 is exactly the same as that of the cutter R except that the teeth 2 are 70 engaged instead of the teeth 1. The distorted shape of the cutter S causes the desired distortion in the shape of the teeth 2 of the cutter A. The cutter S shapes the teeth 2 with the several points 21, 22, 23, 24'

and 25 all at the proper distances from the axis so that these teeth when used will cut the true predetermined contour, as shown by fulllines in Fig. 7

In making the cutter B both cutters R and S may be used, the operation being the same as that shown in Figs. 22 to 25, except that each preliminary cutter engages each tooth of the final cutter. Preferably, however, the cutter T is used, as shown in Figs. 26 to 33. The'cutter .T is shown in Fig. 26 with one of its teeth 46 engaging a tooth 9 of a cutter blank B. For the present let it be imagined that the cutter'T has only the teeth 46 the teeth 49 being omitted. The cutter T is assumed to be rotating rapidly, as indicated, and the blank B is assumed to be rotating slowly in the opposite direction, as indicated. It is also assumed that relative approaching and receding movements are effected between the cutter and the blank in timed relation tothe blank rotation to provide the required relief on the finished tooth. The action of the teeth 46 of the cutter T taken by themselves, is exactly the same as that of the cutter R, as shown in Figs. 22 and 23. The teeth 46 would mill the tooth 9 to' the form shown, this tooth in transverse section having a distorted shape as indicated by dotted-lines in Fig. 6, but nevertheless presenting an effective contour 21, 22, 23, 24, 25 at the cutting face which is correct for cutting the predetermined contour.

Fig. 27 is a view similar to'Fig. 26 but showing the'cutter T with one of its teeth 49 engaging a tooth 10" of the cutter blank B. In considering this figure let it be imaginefl that the cutter T has only teeth 49*, the teeth 46 being omitted. The teeth 49 of the. cutter T, if acting by themselves, would mill the tooth 10" to the form shown. Inasmuch as the cutting faces 51 of the teeth 49 are inclined oppositely to the faces 13 of the are cut with a cross sectional shape which is distorted oppositely to the proper distortion that would be necessary for providing the correct effective contour at the cutting faces. The result is that p the teeth 9" have an abnormally distorted contour 21", 22..' 23,24", 25", at the cutting face, the part 21", 22", 23 being outside the correct contour 21, 22, 23 as shown in Fig, 6,

and the part 23, 24", 25 being inside the correct contour 23, 24, 25 as shown in Fig. 6.

The point 23 of this distorted contour coincides with the point 23 of the correct contour.

Inasmuch as the cutter T actually has both kinds of teeth 46 and 49 and inasmuch as these teeth follow each otherin rapid' 46 reduce the contour 21", 22", 23 which the teeth 49 tend to cut. As the result of the composite action of the two sets of teeth '46 and 49 the teeth 9 are milled 'as shown in Figs. 28 and 29. Each tooth has the same contour 21, 22, 23 as the tooth 9 shown in Fig. 26, and has the same contour from 23, 24 25 as the tooth 9" shown in Fig. 27. The tooth 9 is effective at its right foremost side to cut the part 21, 22, 23 of the predetermined contour as shown in Fig. 6. The outline 23, 24 25" of the cutting face is reduced and will not cut the predetermined contour.

Figs. 30 and 31 are views similar respectively to Figs. 26 and 27 and illustrate the separate actions of the'teeth 49 and'46 in milling one of the teeth 2 of the final cutter A. The teeth 49, if acting by themselves, would mill the tooth 10 to the form shown, this tooth in transverse section having a distorted shape as indicated by dotted. lines in Fig. 7, but nevertheless presenting an effective contour 21, 22, 23, 24, 25 at the cutting face 6, which is correct for cutting the predetermined contour. The teeth 46?, if acting by themselves, would mill the tooth 10" to the form shown. Inasmuch as the cutting faces 48 of the teeth 46 are inclined oppositely to the faces 14 of the teeth 10", the teeth 10" are cut with a cross sectional shape which is distorted oppositely to the properdistortion that would be necessary for providing the correct effective contour at the cutting faces. The result is that the teeth 10 have an abnormally distorted contour 21", 22 23, 24", 25" at the cutting face, the part 23, 24", 25 being outside the correct contour 23, 24, 25 as shown in Fig. 7 and the part 21*, 22 23 being inside the correct contour 21, 22, 23 as shown in Fig. 7. The point 23 of this distorted contour coincides with the point 23 of the correct contour. The tooth 10 cut by the composite action of the teeth 49 and 46" is shown in Figs. 32 and 33. Each tooth has the same contour 23, 24, 25 as the tooth 10 shown in Fig. 30, and has the same contour 21 22 23 as the tooth 10 shown in Fig. 31. The tooth 10 is effective at its left foremost side to cut the part 23, 24, 25 of the predetermined contour, as shown in Fig. 7. The outline 21 22 23 of the cutting edge is reduced and will not cut the predetermined contour.

When the cutter B is used, as already stated, the teeth 1 and 2 follow each other in rapid succession, the teeth 1 cutting the part 21, 22, 23 of the contour and the teeth 2 cutting the part '23, 24, 25 of the contour; Thus the cutter cuts the full predetermined contour, cutting taking place only at the front oblique-angled edges 6, the rear obtuse-angled edges 7' being ineffective.

In my copending application for methods of making milling cutters, Serial No. 286,522, filed on even date herewith I have shown two preliminary milling cutters and also a single preliminary cutter adapted to be used either directly or indirectly for forming the shape of the final cutter. In the said application certain broad claims are presented and also specific claims covering the use of two cutters and also covering the use of the preliminary milling means in conjunction with a non-rotary cutting means.

l. The herein described method of shap-' ing a relieved milling cutter adapted to. cut

a predetermined contour other than a straight line and having different cutting faces oppositely inclined with respect to the axis, the method consisting in forming a preliminary rotary milling means having at planes of intersection transverse to the lines of cutting a shape the same or approximately the same as the predetermined contour, the said preliminary milling means being provided with oppositely inclined cutting faces having adegree of inclination bearing a predetermined ratio to the degree of inclination of the cutting faces of the final cutter and being provided with a degree of relief bearing a ratio to the degree of relief of the teeth .of the final cutter.

which is the inverse of the ratio between the degrees of inclination, and in milling the relieved final milling cutter with the said preliminary milling means whereby the final cutter is formed with distorted shapes at axial planes of intersection back of the respective oppositely inclined cutting faces but is adapted to cut the correct contour when rotated. I

2. The herein described method of shaping a relieved milling cutter adapted to cut apredetermined contour other than a straight line and having different cutting faces oppositely inclined with respect to the axis, the method consisting in forming a single preliminary milling cutter having at The claims of the present application are directed to the use of the prelimi planes of intersection transverse to the lines vided with oppositely inclined cutting faces having a degree of inclination bearing a predetermined ratio to the degree of inclination of the cuttin faces of the final cutter and being pr'ovlded with a degree of relief bearing a ratio to the degree of relief of the teeth of the final cutter which is the inverse of the ratio between the degrees of inclination, and in forming the shape of the relieved final millingcutter from the said preliminary cutter whereby the final cutter is formed with distorted shapes at axial planes of intersection back of the respective oppositely inclined cutting faces but is adapted to cut the correct contour when'rotated.

3. The herein described method of shaping a relieved milling cutter adapted to cut a predetermined contour other than a straight line and having different cutting faces oppositely inclined with respect to the axis, the method consisting in forming a single preliminary milling cutter having at planes of intersection transverse to the lines of cutting a shape the same or approximately the same as the predetermined contour, the said preliminary cutter being provided with oppositely inclined cutting faces having a degree of inclination bearing a predetermined ratio to the degree of inclination of the cutting faces of the final cutter and being provided with a degree of relief bearing a ratio to the degree of relief of the teeth of the final cutter which is the inverse of the ratio between the degrees of inclination, and in milling the relieved final milling cutter with the said preliminary milling cutter whereby the final cutter is formed with distorted shapes at axial planes of intersection back of the respective oppositely inclined cutting faces but is adapted to cut the correct contour when rotated.

4. The herein described inethod of shaping a spirally relieved milling cutter adapted to cut a predetermined contour other than a straight line and having different oppositely inclined helicoidal cutting faces, the method consisting in forming a preliminary rotary milling means having at axial planes of intersection a shape the same or approximately the same as the predetermined contour, the said preliminary milling means being provided with oppositely inclined helicoidal cutting faces each having a longitudinal pitch bearing a predetermined ratio to the longitudinal pitch of the cutting faces of the final cutter and being provided with a degree of spiral relief bearing the same predetermined ratio to the degree of spiral relief of the teeth of the final cutter, and in milling the spirally relieved final milling cutter with the said preliminary milling means whereby the final cutter is formed with distorted shapes at axial planes of intersection back of the respective oppositely inclined helicoidal cutting faces but is I adapted to cut the correct contour when rotated.

5. The herein described method of shaptersection a shape the same or approximately the same as the predetermined con-' tour, the said preliminary milling cutter being provided with oppositely inclined helicoidal cutting faces each having a longitudinal pitch bearing a predetermined ratio to the longitudinal pitch of the cutting faces of the final cutter and being provided with a degree of spiral relief bearing the same predetermined ratio to the degree of spiral relief of the teeth of the final cutter, and in forming the shape of the spirally relieved final milling cutter from the said preliminary cutter whereby the final cutter is formed with distorted shapes at axial planes of intersection back of the respective oppositely inclined helicoidal cutting faces but is adapted to cut the correct contour when rotated.

6. The herein described method of shaping a spirally relieved milling cutter adapted to cut a predetermined contour other than a straight line and having different oppositely inclined helicoidal cutting faces, the method consisting in forming a single preliminary milling cutter having at axial planes of intersection a shape the same or approximately .the same as the predetermined contour, the

said preliminary milling cutter being provided with oppositely inclined helicoidal cutting faces each having a longitudinal pitch bearing a predetermined ratio to the longitudinal pitch of the cutting faces of the 7. The herein described method of shap ing a spirally relieved milling cutter adapted to cut a predetermined contour other than a straight line and having different oppositely inclined helicoidal cutting faces, the method consisting in forming a single preliminary milling cutter having at axial planes of intersection a shape the same or approximately the same as the predetermined contour, the said preliminary milling cutter being vided with oppositely inclined helicoidal procutting faces each having a longitudinal pitch the same as the longitudinal pitch of the cutting faces of the ing provided 5 the same as the degree of teeth of the final cutter,

final cutter and be with a degree of spiral relief spiral relief of the and in milling the spirally relieved final milling cutter With the said pre liminary cutter whereby the final cutter is formed with distorted shapes at axial planes of intersection back of the respective oppositel inclined helicoidal cutting faces but is a apted to cut the correct contour when rotated.

In testimony whereof 1 hereto affix my signature. 7 u 1 FRIEDERICH MULLER. 

